A packaging machine comprising a sealing station is known e.g. from DE 10 2006 018 327 A1, the packaging machine there being a tray sealer. In the sealing station of this packaging machine, a sealing film is applied to the trays which are open at the top and filled with the product in question. This sealing film closes and seals the trays. A corresponding sealing station is also used in thermoformer packaging machines or in chamber machines. Alternatively to sealingly applying a cover film, also a lid, which has already been preformed, may be sealingly applied to the tray or the packaging trough.
For the purpose of sealing, it will be of advantage when underpressure as well as overpressure are available. By means of the underpressure, the packages can be evacuated in the sealing station so as to increase the shelf life of the products. Optionally, the package may be flushed by or filled with an exchange gas after evacuation. The sealing itself is normally executed under the influence of pressure and temperature on the sealing film. To this end, an overpressure source is normally provided, which provides the compressed air used for pressing the sealing tool against the package.
Compressed air and underpressure are also used in other areas of a packaging machine. DE 10 2005 061 315 A1, for example, shows a packaging machine in which overpressure and underpressure are used not in a sealing station but in a thermoforming station. For generating these pressures, a claw vacuum pump is provided.
Such a claw pump is described e.g. in DE 19629174 A1.
Other devices making use of overpressure and underpressure for deforming packaging films, but not for sealing such packaging films, are disclosed by DE 3842135 A1 or CH 332587.